Recently, I've been trying to trace unpublished or hard-to-find letters by Tolkien.

Does anyone happen to know if the Collected Letters of C.S. Lewis contains only letters from C.S. Lewis (like The Letters of JRRT)? I guess this is the case, although the volumes might give a hint of letters sent to Lewis from Tolkien which were not included in The Letters of JRRT.

I have the "Letters of C.S. Lewis" edited by W.H.Lewis first printed in 1966 by Bles.

This is not the same book that you mention, but this book has a couple of problems that relate to your enquiry. It has no index, so it is difficult to find all Tolkien references and it also appears to not have a single letter addressed directly to Tolkien.

The "Collected Letters" edited by Walter Hooper are in three volumes and it looks like volume two may contain some letters sent to Tolkien.

Yes, Lewis's _Collected Letters_ contains only letters written by Lewis. There's one to Tolkien in Volume 2; the one where Lewis praises LotR - 'Uton herian holbytlas', etc. (Oct. 27, 1949). Another is to be found in Vol.3.

Reading Lewis's letters can never be said to be a waste; there's a lot of good stuff in there. And there's quite a few mentions of Tolkien throughout the three volumes. But I can't sift through the great mass to find snippets of what might be letters from T. to L. A better bet, for my money, is Scull and Hammond's two-volume 'JRR Tolkien: A Companion and Guide_ which has parts of many previously unpublished letters - from auction catalogues, for example - and also select extracts from Tolkien's diary. All in all - a must!